House Oversight Committe chairman Darrell Issa is poised to call Internal Revenue Service officials who are based in the agency’s headquarters in Washington, D.C., to testify before his committee next Thursday, July 18, about the targeting of tea-party and other conservative groups.

“This hearing will examine why decisions to elevate cases to more senior levels of the IRS led to unjust delays and unfair treatment of tea-party applications,” the California Republican said in a statement. “The evidence gathered in this investigation makes clear that had Washington IRS officials simply kept their hands off these cases and allowed employees in the Cincinnati office to process applications independently, instead of facing excessive delays, these cases would have been processed just like other advocacy cases.”

While Issa did not reveal the names of the officials who will appear before the commmittee, Oversight investigators have privately interviewed D.C. officials Holly Paz, the head of the IRS’s Rulings and Agreements office who was placed on administrative leave last month, and Carter Hull, the lawyer accused by a Cincinnati employee of micromanaging the processing of tea-party cases.

The question looming over the investigation, however, is whether Issa will demand that Lois Lerner return to Capitol Hill. Last week, Lerner, the embattled former head of the IRS’s exempt-organizations division, demanded immunity in exchange for her testimony after invoking her Fifth Amendment rights at a May 22 Oversight Committee hearing. The panel voted in late June that Lerner had in fact waived her rights by declaring her innocence in an opening statement, and Issa signaled his desire to call her back shortly after that vote. Last week, however, a source familiar with the investigation said the committee had not reached a decision about whether her investigators would need her testimony. In 2011 Lerner expressed awareness of how the onerous questionnaires sent by the IRS, which she defended in a 90-page letter to the Oversight Committee in May of last year, could impact citizens, telling Businessweek that receiving one could serve as a “behavior changer.” (That remark was unearthed earlier today by the conservative blog Patterico.)

The announcement of next week’s hearings comes amidst a slew of scandals at the tax-collection agency, including a report about its lavish spending on an employee conferences, the news that it accidentially disclosed as many as 100,000 Social Security numbers, and the revelation that last year it was paying over 200 employees to work full-time for the National Treasury Employee’s Union. In response, House Republicans have introduced legislation that would, among other things, prevent the agency from enforcing Obamacare and require it to receive congressional approval for government conferences. A vote on the legislation is expected before the August recess.